1. Technical Field
The present invention relates to a transition metal complex and a transition metal catalyst composition comprising the same for the preparation of an ethylene homopolymer or a copolymer of ethylene and α-olefin. More particularly, it relates to a group IV transition metal catalyst having a cyclopentadiene derivative and at least one aryl oxide ligand in which an oxygen-containing heterocycle is fused at the ortho-position around a group IV transition metal, with no crosslinkage between the ligands, a catalyst composition comprising the transition metal catalyst and an aluminoxane cocatalyst or a boron compound cocatalyst, and a process for preparing an ethylene homopolymer or a copolymer of ethylene and α-olefin using the same.
2. Description of the Related Art
Conventionally, Ziegler-Natta catalyst systems comprising titanium or vanadium compounds as main catalyst and alkylaluminum compounds as cocatalyst have been used to prepare ethylene homopolymers or copolymers of ethylene and α-olefin. Although the Ziegler-Natta catalyst system provides good efficiency of ethylene polymerization, the resulting polymers tend to have a broad molecular weight distribution because of the heterogeneousness of catalytic active sites. In particular, the compositional distribution is not uniform for a copolymer of ethylene and α-olefin.
Recently, the so-called metallocene catalyst system, which comprises metallocene compounds of group IV transition metals, e.g. titanium, zirconium or hafnium, and methylaluminoxane as cocatalyst, has been developed. Because this catalyst system is a homogeneous cocatalyst having homogeneous catalytic active sites, it is capable of preparing polyethylenes having a narrower molecular weight distribution and a more uniform compositional distribution as compared to the Ziegler-Natta catalyst system. For example, European Patent Publication Nos. 320,762 and 372,632 or Japanese Patent Laid-Open Nos. Sho 63-092621, Hei 02-84405 and Hei 03-2347 disclose that polyethylenes having a molecular weight distribution (Mw/Mn) of 1.5-2.0 can be prepared efficiently from ethylene by activating the metallocene compounds Cp2TiCl2, Cp2ZrCl2, Cp2ZrMeCl, Cp2ZrMe2, ethylene (IndH4)2ZrCl2, etc. with the cocatalyst methylaluminoxane. However, it is difficult to obtain high molecular weight polymers with this catalyst system. Especially, when applied to solution polymerization performed at high temperature, i.e. 140° C. or higher, it is not suitable to prepare high molecular weight polymers having a weight average molecular weight (Mw) of 100,000 or larger because the polymerization efficiency decreases rapidly and β-hydrogenation dominates.
Recently, the so-called geometrically constrained non-metallocene catalyst system (also known as the single-site catalyst) enabling the preparation of high molecular weight polymers through homopolymerization of ethylene or copolymerization of ethylene and α-olefin under the solution polymerization condition, in which a transition metal is connected as a ring. European Patent Publication Nos. 0416815 and 0420436 disclose a compound in which an amide group is connected to a cyclopentadiene ligand to form a ring. And, European Patent Publication No. 0842939 discloses an electron donor compound catalyst in which a phenol-based ligand and a cyclopentadiene ligand are connected to form a ring. However, the geometrically constrained catalyst is inappropriate for commercial application because the yield of the ring forming reaction between the ligand and the transition metal compound in the synthesis of the catalyst is very low.
U.S. Pat. No. 6,329,478 and Korean Patent Publication No. 2001-0074722 disclose non-geometrically constrained, non-metallocene catalysts. These patents disclose that single-site catalysts having at least one phosphinimine compound as ligand provide superior ethylene transition ratio during the copolymerization of ethylene and α-olefin by solution polymerization under high temperature condition of 140° C. or higher. U.S. Pat. No. 5,079,205 discloses a catalyst having a bisphenoxide ligand, and U.S. Pat. No. 5,043,408 discloses a catalyst having a chelate type bisphenoxide ligand. However, these catalysts have too low a catalytic activity to be commercially applicable in the preparation of an ethylene homopolymer or a copolymer of ethylene and α-olefin carried out at high temperature.
Japanese Paten Laid-Open Nos. 1996-208732 and 2002-212218 disclose a use of a catalyst for olefin polymerization having an anilido ligand. But, the patents do not state preparation in a commercially meaningful polymerization temperature range. Further, the catalyst is structurally different from the transition metal catalyst presented by the present invention having an anilido ligand with an aryl substituent at the ortho-position. In addition, although use of an anilido ligand as non-metallocene catalyst for polymerization is reported by Nomura et al. [Organometallics 2002, 21, 3043], the relevant substituent is simply limited methyl.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the related art that is already known in this country to a person of ordinary skill in the art.